The present invention relates to a method and installation for loading and unloading compressed natural gas onto and off ships.
Unlike shipping natural gas in a liquid form which requires major technical facilities, including for lowering its temperature to the temperature of liquefaction of −163° C., shipping natural gas in a compressed form is, for short distances, much more economical. In this process the natural gas is stored in tubes in which it is compressed to between 200 and 300 bar and the ships have receiving means to which said tubes are fixed.
The ships are thus suitable for shipping compressed natural gas from a loading zone somewhere near an off-shore field, for example, to an unloading zone, such as a port installation.
However, one problem with this method is the amount of time the ships are immobilized while the tubes are loaded or refilled and unloaded or emptied. The ships cannot be other than immobilized throughout the unloading process, which can take several days.
One particular document that may be referred to is EP 0 333 951, which discloses a tube-carrying ship for carrying out just such a method.
One problem that arises, and to which the present invention seeks to provide a solution, is therefore the provision of a method and installation for loading and unloading compressed natural gas that reduces ship immobilization time and therefore reduces the costs of shipping natural gas between the field and the port installation.